Regulation Text
Unless otherwise authorized by ATC, no person may operate an aircraft within controlled airspace under IFR except as follows:
(a) On an ATS route, along the centerline of that airway.
(b) On any other route, along the direct course between the navigational aids or fixes defining that route. However, this section does not prohibit maneuvering the aircraft to pass well clear of other air traffic or the maneuvering of the aircraft in VFR conditions to clear the intended flight path both before and during climb or descent.
[Docket 18334, 54 FR 34294, Aug. 18, 1989, as amended by Amdt. 91-296, 72 FR 31679, June 7, 2007]
The short answer
(14 CFR § 91.181) Unless otherwise authorized by ATC, no person may operate an aircraft within controlled airspace under IFR except along the centerline of an ATS route, or along the direct course between the navigational aids or fixes defining any other route. Maneuvering to pass clear of traffic or to clear the flight path in VFR conditions is permitted.
Research Notes
Common Questions
What course must an IFR aircraft fly on an ATS route?
It must fly the centerline of that airway unless ATC authorizes otherwise.
“(a) On an ATS route, along the centerline of that airway.” — 14 CFR § 91.181(a)
What course applies on a route that is not an ATS route?
The aircraft flies the direct course between the navigational aids or fixes defining that route.
“(b) On any other route, along the direct course between the navigational aids or fixes defining that route.” — 14 CFR § 91.181(b)
Does this rule prevent maneuvering to avoid traffic?
No — it does not prohibit maneuvering well clear of traffic or clearing the flight path in VFR conditions.
“this section does not prohibit maneuvering the aircraft to pass well clear of other air traffic or the maneuvering of the aircraft in VFR conditions to clear the intended flight path both before and during climb or descent.” — 14 CFR § 91.181(b)
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